1. Field of the Invention
The present invention relates to a polypropylene resin composition and an injection molded article thereof. More particularly, the present invention relates to a polypropylene resin composition which provides a injection-molded article with excellent rigidity and thermal resistance, and small anisotropy of mold shrinkage coefficient of the mold article, and to an injection molded article comprising the polypropylene resin composition.
2. Description of Related Art
A polypropylene resin is light in weight, and excellent in mechanical properties and moldability. The resin is, therefore, has been used widely in various application fields. As a method for improving the mechanical properties, use of a nucleating agent is known.
For example, JP10-306181A discloses that a polypropylene resin composition mainly containing crystalline polypropylene with degrees of b-axis orientation of more than 720 as determined by the ratio of intensities of specified diffraction peaks measured by wide angle X-ray diffraction taken in the vicinity of the central portion of an ASTM No. 1 dumbbell specimen prepared by injection molding, an excellent moldability and good mechanical properties.
In recent years, however, applications of polypropylene resin composition has been enlarged, conventional polypropylene resin compositions are insufficient in rigidity and thermal resistance for an application, and particularly, in large molded articles, deformation or warp sometimes generates. It is considered that one of the reason for these phenomena is ascribed to anisotropy of mold shrinkage coefficient of the mold article, and hence an improvement of these characteristics have been desired.
An object of the present invention is to provide a polypropylene resin composition which can provide an injection molded article having excellent rigidity and thermal resistance, and a small anisotropy of mold shrinkage coefficient, and an injection molded article comprising said polypropylene resin composition.
As a result of extensive studies, the inventors have found that a polypropylene resin composition containing both of a specified nucleating agent (a) in a specific amount range and another specified nucleating agent (b) in a specific amount range and having orientation degrees (A) and (B) determined by wide angle X-ray diffraction of the injection molded article of the composition in specified ranges, respectively, could solve the above problems, and have completed the present invention.
Namely, the present invention relates to a polypropylene resin composition which comprises 100 parts by weight of a propylene homopolymer, 0.01 to 1.0 part by weight of phosphoric acid ester type nucleating agent (a) (hereinafter, sometimes referred to as xe2x80x9cnucleating agent (a)xe2x80x9d) and 1.5 to 5 parts by weight of talc (b) (hereinafter, sometimes referred to as xe2x80x9cnucleating agent (b)xe2x80x9d), wherein the composition satisfies the following condition(1):
(1) the injection molded article of the polypropylene resin composition has degrees of orientation A and orientation B measured by wide angle X-ray diffraction of not less than 35 and not less than 300, respectively.
Further the present invention is related to an injection molded article comprising the polypropylene resin composition.
The present invention will be described in detail below.